Tank for liquified gases

ABSTRACT

A storage tank, for liquified gases, having intersecting side wall plates and being lined with a layer of heat-insulating material which forms a smoothly curving bulge directed toward the interior of the tank from any corner thereof.

United States Patent v [191 Beau jean Sept. 9, 1975 TANK FOR LIQUIFIED GASES [75] Inventor: Joseph M. E. Beaujean, Amsterdam,

Netherlands [73] Assignee: Shell Oil Company, Houston, Tex. [22] Filed: Feb. I9, 1974 [21 Appl No.: 443,549

[30] Foreign Application Priority Data Feb. 23, 1973 Netherlands 7302527 [52] US. Cl. 220/63 R; 29/490; 220/9 LG [5 [1 Int. Cl. B65D 87/34; 8638 3/64 [58] Field of Search r. 220/9 R, 9 A, 9 F, 9 LG, 220/63 R; ll4/74 A; [56/78; I l7/l04 R; 29/490 [56] References Cited UNITED STATES PATENTS 3 l5(l 794 9/1964 Schlumbcrger ct alv 220/9 LG 3,67l,3l5 6/l972 larossi .r 220]; LG

FOREIGN PATENTS OR APPLICATIONS [434.942 3/1966 France .r 114/74 A l,l3l,024 10/1968 United Kingdom H l4/74 A Primary ExaminerWilliam l. Price Assislan! ExaminerStephen Marcus [57] ABSTRACT A storage tank, for liquified gases, having intersecting side wall plates and being lined with a layer of heatinsulating material which forms a smoothly curving bulge directed toward the interior of the tank from any corner thereof 14 Claims, 5 Drawing Figures PATENTED SEP 9 75 SHEET 1 OF 2 FIG] PATENTEB SEP 9 I975 SHEET 2 UP 2 TANK FOR LIQUIFIED GASES BACKGROUND OF THE INVENTION The invention relates to a tank for the storage of liquified gases, comprising a rigid outer shell internally lined with a heat-insulating foam layer, which outer shell has at least two intersecting planes. A tank of this type is known, for example, from the patent specification pertaining to applicants UK. patent l,l73,424. The tank known from the said patent specification is prismatic in shape, in other words this tank has a rigid outer shell with at least two intersecting planes.

When tanks of this type are used for the storage of very cold liquids, for example for liquified natural gas, there is a risk that cracks will develop in the foam layer near the location where the two planes of the rigid outer layer intersect. This risk of cracking is caused by the local occurrence of high tensile stresses in the foam layer. These high tensile stresses are caused by the cooling down of the foam layer by contact with the cold liquid and by the hydrostatic pressure exercised locally by the cold liquid on the foam layer.

It is the object of the invention to reduce considerably this risk of cracking of the foam layer.

SUMMARY OF THE INVENTION According to the invention, the foam layer, near the location where the two planes of the rigid outer shell intersect, forms a substantially smoothly curving bulge directed towards the interior of the tank.

More particularly, the invention is characterized in that, viewed in an intersection plane perpendicular to the intersection line of the two intersecting planes of the outer shell, the heat-insulating foam layer appears as a substantially smoothly curving strip having at least two bends (a), the concave sides of which are directed towards the interior of the tank.

In an attractive embodiment of the invention, the said strip also has a bend (b) of which the concave side is directed towards the exterior of the tank, which bend (b) is situated between the said bends (a).

The bulge in the foam layer according to the invention yields the advantage that the foam is free to shrink on cooling down and that, owing to the chosen local shape of the foam layer, the hydrostatic pressure will locally cause compressive stresses in the foam layer, instead of tensile stresses as in the conventional constructions. As a result, the tensile stresses in the foam layer (caused by cooling) and the compressive stresses in the foam layer (caused by hydrostatic pressure) will be equalized.

BRIEF DESCRIPTION OF THE DRAWING The invention will be further elucidated with reference to the drawings, in which:

FIG. I shows a transverse cross-section of a prismatic tank constructed according to the invention;

FIG. 2 is an enlarged representation of the part encompassed by the circle II in FIG. 1',

FIG. 3 shows the invention in perspective, where three planes of the outer shell intersect in a single point, said point forming a corner of the tank. This is, for example, an enlarged representation of the part encompassed by the circle III in FIG. 4;

FIG. 4 shows diagrammatically a prismatic tank in perspective, to which the invention may be applied.

FIG. 5 shows diagrammatically a cylindrical tank in perspective, to which the invention may be applied.

In the FIGS. 1-3 the rigid outer shell of the tank is designated by the reference numeral I. This rigid outer shell may be formed in the case of a ship, for example, by the steel walls of the ship's hold. In marine tankers for the transportation of liquified gases, such as liquified natural gas or methane, which tankers are generally of the double-hull type, the rigid outer shell is formed by the inner hull of the ship. In that case the rigid outer shell has at least two intersecting planes.

A pair of such intersecting planes are designated by the reference numerals 2a and 2b. The interior of the rigid outer shell I is lined with a heat-insulating foam layer 3. The latter may, for example, be a suitable plastic material, for example hard (rigid) polyurethane foam applied for example by a spraying method.

In FIG. 2, a part of a pair of intersecting planes 2a and 2b of the rigid outer shell is shown in a crosssection taken perpendicular to the intersection line of the two planes 2a and 2b. As is clearly shown by FIG. 2, the foam layer 3, near the location where the two planes 2a and 2b intersect, forms a substantially smoothly curving bulge directed towards the interior of the tank. In the cross-section shown in FIG. 2, the foam layer 3 appears as a strip curving smoothly from plane 20 to plane 212. This strip has two bends (a) of which the concave sides are directed towards the interior of the tank. Between the bends (a) the strip has a bend (b) of which the concave side is directed towards the exterior of the tank. In an attractive embodiment of the invention, the two bends (a) are situated substantially symmetrically with respect to the bi-sectrix of the angle formed by the two intersecting planes 2a and 2b. Preferably, the bend (b) is also situated symetrically with respect to the said bi-sectrix.

The two bends (a) preferably have the same curvature radius R,. The curvature radius R of the bend (b) is preferably greater than the curvature radius R, of the bends (a R however, is equal to at most 2 R The dz... -e enclosed by the two intersecting planes 2a and Ti the heat-insulating foam layer 3 may be left emp' uowever, it is also possible to fill up this space with a filling material 4. If E, is the modulus of elasticity of the filling material 4 and E, the modulus of elasticity of the filling material 4 and E the modulus of elasticity of the material of the foam layer 3, the materials should preferably be so chosen that E,. E, For the filling material 4 use may be made, for example, of elastic or rigid polyurethane, optionally in the form of foam. Other suitable materials may also be used as the filling material 4.

The foam layer 3 is preferably bonded to the interior surface 7 of the filling material 4. If the filling material 4 is for example polyurethane foam (rigid or elastic) and if the foam layer 3 is rigid polyurethane foam, the layer 3 may be simply sprayed on to the interior surface 7 of the filling material 7. As a result a fixed connection will be produced between the foam 3 and the filling material 4.

With reference to FIG. 2 the essence of the invention has been explained with a description of the application of the invention in the case of two intersecting planes 2a and 2b. In the case of a prismatic tank, for example of the type as shown diagrammatically in FIG. 4, three planes 2a, 2b and 2c intersect at one point, forming a comer of the tank. This comer, encompassed by the circle III, is enlarged and shown in perspective in FIG. 3. Each pair of intersecting planes 2b and 2c; 20 and 2b, and 2a and 2c is provided with a foam layer 3 and near the location where each pair of these planes intersect the foam layer 3 forms the smoothly curving bulge directed towards the interior of the tank, according to the invention and as fully described with reference to FIG. 2.

In FIG. 3 the bulge in the foam layer associated with the pair of planes 2b and 2c is designated by the reference numeral 8, that associated with the pair of planes 2a and 2b by the reference numeral 9, and that with the pair of planes 2a and 20 by the reference numeral 10. The bulges 8, 9 and 10 gradually merge near the corner and form a common bulge 11 which is directed towards the interior of the tank.

FIG. 5 shows a diagrammatic representation of a cylindrical tank. Here too, the invention may be applied with advantage, for example Where the lateral area plane 6a and the bottom plane 6b of the cylinder intersect.

] claim as my invention:

1. A tank for the storage of liquified gases, comprising a rigid outer shell internally lined with a heatinsulating foam layer, which outer shell has at least two intersecting planes, characterized in that the foam layer at the location where the two planes of the rigid outer shell intersect, forms a substantially smoothly curving bulge directed towards the interior of the tank,

2. A tank as claimed in claim 1, characterized in that the heatinsulating foam layer consists of foamed plastic.

3. A tank as claimed in claim 2, characterized in that the heatinsulating foam layer consists of hard polyurethane foam.

4. A tank as claimed in claim 1, characterized in that, viewed in an intersection plane perpendicular to the intersection line of the two intersecting planes of the outer shell, the heat-insulating foam layer appears as a substantially smoothly curving strip having at least two bends (a), the concave sides of which are directed towards the interior of the tank.

5. A tank as claimed in claim 4, characterized in that the two bends (a) are situated substantially symmetrically with respect to the bi-sectrix of the angle formed by the two intersecting planes of the outer shell.

6. A tank as claimed in claim 4, characterized in that the two bends (a) have the same curvature radius R,.

7. A tank as claimed in claim 4, characterized in that the said strip also has a bend (b) of which the concave side is directed towards the exterior of the tank, which bend (b) is situated between the bends (a).

8. A tank as claimed in claim 7, characterized in that the bend (b) is situated substantially symmetrically with respect to the bi-sectrix of the angle formed by the two intersecting planes of the outer shell.

9. A tank as claimed in claims 7, characterized in that bend (b) has a curvature radius R R being 2R,.

10. A tank as claimed in claim 1, characterized in that the space enclosed by the two intersecting planes of the outer shell and the heat-insulating foam layer at the locus of the bulge is filled with a filling material.

11. A tank as claimed in claim 10, characterized in that the filling material has a modulus of elasticity of E, and that the material of the heat-insulating foam layer has a modulus of elasticity of E,, B, being smaller than E,.

12. A tank as claimed in claims 10, characterized in that the filling material is fixed to the heat-insulating foam layer.

13. A tank as claimed in claim 10, characterized in that the filling material is a foamed plastic.

14. A tank as claimed in claim 13, characterized in that the filling material is polyurethane foam. 

1. A tank for the storage of liquified gases, comprising a rigid outer shell internally lined with a heat-insulating foam layer, which outer shell has at least two intersecting planes, characterized in that the foam layer at the location where the two planes of the rigid outer shell intersect, forms a substantially smoothly curving bulge directed towards the interior of the tank.
 2. A tank as claimed in claim 1, characterized in that the heatinsulating foam layer consists of foamed plastic.
 3. A tank as claimed in claim 2, characterized in that the heatinsulating foam layer consists of hard polyurethane foam.
 4. A tank as claimed in claim 1, characterized in that, viewed in an intersection plane perpendicular to the intersection line of the two intersecting planes of the outer shell, the heat-insulating foam layer appears as a substantially smoothly curving strip having at least two bends (a), the concave sides of which are directed towards the interior of the tank.
 5. A tank as claimed in claim 4, characterized in that the two bends (a) are situated substantially symmetrically with respect to the bi-sectrix of the angle formed by the two intersecting planes of the outer shell.
 6. A tank as claimed in claim 4, characterized in that the two bends (a) have the same curvature radius R1.
 7. A tank as claimed in claim 4, characterized in that the said strip also has a bend (b) of which the concave side is directed towards the exterior of the tank, which bend (b) is situated between the bends (a).
 8. A tank as claimed in claim 7, characterized in that the bend (b) is situated substantially symmetrically with respect to the bi-sectrix of the angle formed by the two intersecting planes of the outer shell.
 9. A tank as claimed in claims 7, characterized in that bend (b) has a curvature radius R2, R2 being < or = 2R1.
 10. A tank as claimed in claim 1, characterized in that the space enclosed by the two intersecting planes of the outer shell and the heat-insulating foam layer at the locus of the bulge is filled with a filling material.
 11. A tank as claimed in claim 10, characterized in that the filling material has a modulus of elasticity of Ev and that the material of the heat-insulating foam layer has a modulus of elasticity of Es, Ev being smaller than Es.
 12. A tank as claimed in claims 10, characterized in that the filling material is fixed to the heat-insulating foam layer.
 13. A tank as claimed in claim 10, characterized in that the filling material is a foamed plastic.
 14. A tank as claimed in claim 13, characterized in that the filling material is polyurethane foam. 